A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
The present invention relates to a method and apparatus for the measuring of power and current flowing through transmission lines, and of the power generation or consumption of a facility.
As the traditional monopolies of electric utilities have been relaxed in the United States, there has developed a growing market in wholesale electric energy. Utilities, independent power producers, and power marketers are some of the participants in this volatile market. Among other variables, such as time of day and year, and temperature, electricity pricing in a given region is dependent on the operational status of the electric generation and use facilities in that region, and the transmission capacity of critical transmission paths.
Participants in the electric power markets, accordingly, would find real-time information on the operational status of important generation, use, and transmission facilities in a region to be useful in developing trading strategies and responses to power system events. Likewise, relaxation of the monopoly status of traditional utilities has resulted in increased competition for customers amongst suppliers of electric energy. Information on the electric power use of potential customers would be useful to those involved in bidding for electricity supply contracts. It would be further advantageous to determine information on the supply and demand of electric energy without having to directly connect to the transmission and distribution lines conducting electric energy.
It is, therefore, an object of the present invention to provide a methodology whereby real-time information on transmission line power flow, generation facility power output, substation power input and output, and facility power use may be obtained remotely and transmitted to an end-user of such information. It is also an object of this invention to provide an apparatus capable of accomplishing this task. It is a further object of this invention to collect and provide this information accurately, regardless of changing environmental conditions, over the long-term, and with a minimum of human involvement. Furthermore, it is an object of this invention to provide this information to an end-user in such a form as to permit the end-user to act in a logical and timely fashion to real-time events on the power system.
Towards the accomplishment of these objects, disclosed is a method for determining in real-time the net electric power and current either generated or consumed by a facility or substation, and the electric power and current transported by an electric transmission line. This is accomplished, in part, through the use of one or more apparatuses for monitoring the magnitude and direction of electric power or current flow in a single electric current carrying conductor or in multiple current carrying conductors operating in a poly-phase arrangement. The present invention thus relates generally to a method and apparatus for the long-term, real-time, remote monitoring of the electric power and current flow to, from, or in a monitored facility.
For the purpose of the following discussion, the terms xe2x80x9ctransmission linexe2x80x9d and xe2x80x9celectrical linexe2x80x9d will generally refer to a set of at least three conductors operated in a poly-phase arrangement for the purpose of transmitting electric energy. Each of the three conductors comprising the transmission line is energized with a sinusoidal voltage 120 degrees out of phase with the other two conductors comprising the transmission line. xe2x80x9cBundledxe2x80x9d conductors, which consist of multiple wires in close proximity to one another that are operated electrically in parallel, will be referred to and treated as a single conductor.
Current and power monitoring according to the present invention may be accomplished by placing one or more of the apparatuses described herein in proximity to each of the electrical transmission lines that provide service to a monitored facility. Generally, it is desired that an apparatus be located within approximately 200 feet of the monitored line, though the actual location of the apparatus is dependent on terrain, line geometry, and other factors unique to the particular line. It is to be understood that the present invention may be used to measure characteristics from single or multiple lines, instead of a facility.
Each individual apparatus transduces magnetic fields emanating from the monitored power line and determines the phase relationship to another signal that is synchronized to power system frequency. This signal, in an exemplary embodiment, may be the electric field emanating from the monitored line. It may also be a measure of the voltage derived from some electrical connection to the power system such as that obtained from an electrical wall outlet. By this synchronization, a measure of the direction of current flow in the line is determined. Because any given distribution or transmission line is operated at near uniform voltage, a measure of the current flow in a line is also a measure of the complex power flow in the line. The power flow can be divided into its real and reactive components through use of the phase angle relationship between the monitored magnetic fields and the synchronized signal.
Standard transmission or distribution lines typically consist of at least three current carrying conductors. Multiple monitoring devices devoted to each line may give increased sensitivity in determining the current flow in the individual conductors using methods such as that described in U.S. Pat. No. 5,438,256, the disclosure of which is hereby incorporated by reference. However, because the method of operation of most transmission lines is predictable, it is possible to monitor a single poly-phase line with a single apparatus, as disclosed herein. Furthermore, multiple poly-phase circuits that are carried on the same transmission structure may be individually monitored using the apparatus and methods disclosed herein.
In an exemplary embodiment of the present invention, magnetic fields may be transduced either through the use of coil probes or Hall effect sensors. Electric fields may be transduced through the use of a free-body meter, or a ground-reference type meter, as described in IEEE Standard 644-1994.
After transduction, signals representing the electric and magnetic field strength may be magnified and filtered. The magnitudes and relative phase angles of these signals are then converted to digital signals, evaluated, and, in an exemplary embodiment, stored by use of a microcontroller or microprocessor, at least one analog to digital (A/D) converter, and digital memory. The microprocessor may be programmed to analyze and record the data received through the A/D converter.
Included in an exemplary embodiment of the apparatus according to the present invention is a device that permits communication between the remote apparatus and a central computing facility. This communication device may comprise, for example, a cellular telephone and modem connected to the microcontroller. Similarly, a radio-frequency, or microwave connection may be made between the apparatus and the central computing facility. Satellite communication between the apparatus and the computing facility is also realizable. Algorithms in the microcontroller determine when and if the apparatus should communicate with the central computing facility, or provide some other form of communication, such as an event-notification alarm, directly to an end-user.
Where environmental concerns exist, the apparatus may include an enclosure that protects the components of the apparatus from the elements. This enclosure may be constructed of material that will not interfere with the strength or the measurement of electric or magnetic fields, such as wood, fiberglass, plastic, or the like. Likewise, if low temperatures are likely to interfere with proper operation of the apparatus, a heating element may be included in the enclosure. The apparatus may be battery powered and may include a solar charger to permit long-term, unattended operation.
The central computing facility may be comprised of a digital computer such as a typical PC and at least one communications device. The central computing facility receives communications from all of the remote apparatuses monitoring a facility, facilities, line, or lines under measurement. The data received from the apparatuses is processed to determine the magnitude and direction of current and power flow in each monitored line. The net power and current flow into or out of the facility may then be calculated as the sum of the individual line flows. Once computed, the net facility power-use or generation, as well as the power and current flows in individual lines can be transmitted in a secured fashion to the end-user. This communication could be made via a direct computer-computer connection, a digital pager, Internet, LAN, WAN, or the like. The central computing facility may provide additional communications such as event-notification-alarms after the recorded data has been analyzed and found to meet certain prescribed conditions.
In a broad aspect, the present invention may include an apparatus for remotely measuring current in an electrical line (or lines) comprising: a magnetic transducer to convert the magnetic field of the current at a remote location, into a magnetically transduced signal; and a first conditioning circuitry coupled to the magnetic transducer to prepare the magnetically transduced signal for analysis. In an exemplary embodiment, the conditioning circuitry may include some or all of the following elements: an amplifier(s); a filter(s), a rectifier(s), all of which may be serially coupled. Of course, multiple apparatuses may be used to measure a plurality of lines.
In exemplary embodiments, the apparatus may also include an electrical transducer to convert the electric field of the line at the remote location into a reference signal; and second conditioning circuitry coupled to the electrical transducer to prepare the reference signal for analysis. Alternately, the reference signal may be synchronized to a frequency of a power system connected to the line. Also, the present invention may include one or more measuring circuits coupled to the conditioning circuits to evaluate magnitude of the magnetically transduced signal and/or phase angle between the magnetic field and reference signal.
Further, an apparatus according to the present invention may include additional elements, including a data storage device to store data, one or more communication devices to transmit the data to a central facility (for processing, maintenance, or further distribution) and/or end users. In exemplary embodiments, the magnetic transducer may comprise a coil probe or a Hall effect sensor, and the electrical transducer may comprise a free-body meter or a ground-reference meter.
Another broad aspect of the present invention includes a method for remotely measuring current in an electrical line (or lines), comprising the steps of placing one or more apparatuses including a magnetic transducer in proximity to the line; receiving magnetic field emanating from the electrical line with the magnetic transducer; and processing the magnetic field to determine a magnitude of the current. Data representative of the magnetic field may be relayed to a central station for some or all of the processing. Further, information representative of the current (i.e., magnitude and/or direction) may be transmitted (via different mediums including, fax, computer, modem, Internet, LAN, WAN, or the like) to an end user.
In addition to the magnetic field, an electrical signal synchronized to a frequency of a power system connected to the line (which may be an electric field emanating from the line, or it may be obtained from a wall outlet), for example) may be received and used to determine a phase angle between the magnetic field and the electrical signal to ascertain the current""s direction.
In certain embodiments, the line may be coupled to a facility, and the information informs the end user of power consumption or power generation of the facility (including net current power flow in a plurality of lines connected thereto).
It has only been recently that there have developed markets for the wholesale trading of electric energy. The power marketers, independent power producers, and others who participate in this market are finding that transmission line loading and the operational status of electric generation and use facilities in a region are important in determining the price and quantity of electricity traded in a region. Access to such information is limited. Utilities operating power systems have always required precise knowledge of transmission line current and power flows, and facility power usage or generation in order to best operate the power system. These utilities have access to the conductors comprising the transmission lines and the equipment to which they are connected. Consequently, systems have been developed that attach directly to electrical line conductors and measure very precisely the current and power flow in the conductor. However, generally, the information from these systems is withheld from market participants.
Because the electric power markets are dependent on the physical status of important facilities and lines, there is a clear market need for the collection and dissemination of operational information regarding said lines and facilities. One of the objects of the present invention is to provide a system to allow the collection and transmission of such information to market participants without connecting to the utility system or requiring the placement of equipment in utility right-of-ways or easements. The present invention accomplishes this by disclosing an apparatus that may be located a distance from a transmission line under surveillance to be used to measure remotely the current or power flow. The method by which information from such an apparatus is used to determine the transmission line current is also disclosed. Additionally, the present invention describes a method for using such information to determine the net power generation or use (or current flow) to or from a monitored facility. All of this information is collected in an automated way that allows for a minimum of required human intervention and is thus well-suited for the long-term, real-time collection of information desired by power market participants. The information may be centrally collected, processed, and then sent in a useful form to a plurality of market participants.
Given the ease of computer to computer communications and the familiarity that market participants already have with computer based information systems, such information may be sent via the Internet, or a LAN, WAN, or the like, to a computer where such information could be displayed to an end-user. The end-user could choose to dedicate a computer monitor or monitors to the display of such information. The system may allow the end-user to view a graph of the power and current flow in a particular transmission line, or set of transmission lines. Similarly, the system may allow the end-user to monitor a graph of the flow of power into or out of a monitored facility or facilities. Such information could be viewed as the information is updated. The system may also provide the end-user a xe2x80x9csnap-shotxe2x80x9d view of the operational status of lines or facilities at a single moment in time. Information may be stored so that historical patterns and trends could be used to develop trading strategies.
Events, such as the outage of a generation, transmission, or use facility, unexpected or otherwise, may be highlighted to the end-user through the use of event notification alarms sent either from the central computing facility, or directly from the distributed monitors. A transmission line reaching its operational limits might also result in an alarm. Such alarms could consist of computerized audible and/or visual warning on the dedicated monitor(s). Additionally, warnings could be sent to a pager or telephone. The alarms could inform the end-user of the date, time and nature of the event.
Information updates to the end-user may be dependent on the transmission of data from the distributed monitors to the central computing facility. Data from an individual monitor may be sent either continuously or after a fixed amount of time has transpired since the last data transmission. Additionally, the monitor may be programmed to transmit data when other conditions are met such as a rapid change in the collected data or the penetration of some threshold. For example, the monitor might immediately transmit data when this data falls below a threshold value suggestive of a transmission line outage. The data may also be processed by the central computing facility to immediately transmit the location and nature of the event and its significance to the end-user, allowing the end-user to act on this knowledge in a timely fashion. Likewise, the end-user may have the option of requesting information from a particular monitor or set of monitors.
Through the use of state-estimation techniques, the power flow information collected by multiple monitoring apparatuses may be used to predict or estimate the power flow, generation, or consumption in other parts of the power system not directly monitored by these apparatuses. State-estimation is a mathematical process and may be performed at the central computing facility. The results can then be transmitted to an end-user of this information. An apparatus in accord with the present invention may also be used to measure, at a given location from a line, the strength of the magnetic field emanating from the line. Such information may be useful, as long-term exposure to magnetic fields may raise health concerns.